1. Field of the Invention
The present invention relates to a drill structure, particularly to a drill structure suitable to be used in printed circuit boards.
2. Description of the Prior Art
Under the trend toward fabricating small, slim and lightweight electronic products, the elements of electronic products grow finer and finer. Thus, the printed circuit board (PCB) where the electronic elements are installed also becomes smaller and smaller. Therefore, the manufacturers require the micro drills used in PCB to have higher precision, strength, feed rate, and surface finish. In practical fabrication, the manufacturer is likely to stack a plurality of PCB's and drills them simultaneously so as to increase the fabrication efficiency and decrease the fabrication cost. In such a case, the micro drill needs to have longer length and sufficient chip discharge capability.
A conventional micro drill involves a shank part and a flute part connected with the shank part. The front end of the flute part has a cutting structure 10, as shown in FIG. 1. The cutting structure 10 includes two primary relief surfaces 12, 12′ and two secondary relief surfaces 14, 14′, which are symmetrically arranged with respect to a static tip point 16 and used to cut workpieces. In such a cutting structure 10, two primary relief surfaces 12, 12′ and two secondary relief surfaces 14, 14′ have a larger contact area with the board, which makes the cutting faces break easily, not only degrading the surface finish of the drilled holes but also shortening the service life of the drill.